1. Field of the Invention
This invention relates to digital transmission systems, in particular, though not exclusively, submarine digital transmission systems.
2. Background Information
Such systems include a first terminal and a second terminal each having a signal transmit means and a signal receive means, a first transmission bearer and a second transmission bearer, the first transmission bearer conveying signals from the signal transmit means of one terminal to the signal receive means of the other terminal, and the second transmission bearer conveying signals from the signal transmitter of the other terminal to the receive terminal of the said one terminal, each bearer having a plurality of spaced regenerators to restore the original shape of a pulse signal transmitted from a signal transmit means of a terminal.
Such transmission systems require a fault location arrangement to locate faults in remote regenerators and in sections of bearer adjacent thereto.
Techniques for locating faults are known and may comprise an arrangement in which a command signal is sent from a terminal of the system which addresses a particular regenerator. The regenerator responds with a status message or an action such as switching a laser or activating a loop-back circuit.
These known arrangements are relatively complicated and require complex circuitry.